Imaging device and interchangeable lens arranged to have a reduced amount of magnetic field reaching an image pickup element

ABSTRACT

A first magnetic body is arranged between a coil and an image pickup element, and has an opening through which light directed from an imaging optical system toward the image pickup element passes. A second magnetic body is arranged at a position on the coil side with respect to the first magnetic body in an optical axis direction of the imaging optical system. The second magnetic body is arranged such that at least a portion thereof overlaps the first magnetic body when seen in the optical axis direction, at a position on the coil side with respect to the opening. The second magnetic body is made of a ferromagnetic material having higher relative permeability than that of the first magnetic body, and has a smaller area than that of the first magnetic body when seen in the optical axis direction.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/720,583, filed on May 22, 2015, entitled “IMAGING DEVICE ANDINTERCHANGEABLE LENS ARRANGED TO HAVE A REDUCED AMOUNT OF MAGNETIC FIELDREACHING AN IMAGE PICKUP ELEMENT”, the content of which is expresslyincorporated by reference herein in its entirety. This application alsoclaims priority from Japanese Patent Application No. 2014-109036 filedMay 27, 2014, which is hereby incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure relates to a technology of suppressing enteringof leakage magnetic field noise, generated from a magnetic fieldgeneration source, into an image pickup element.

Description of the Related Art

Recently, an image pickup element mounted on an imaging device such as adigital camcorder or a digital still camera has higher ISO sensitivity.As such, a clearer image can be taken even in a scene of few lightquantities such as night view. Along with improvements in sensitivity,however, an image pickup element is affected by weak noise which has notbeen a problem, whereby a problem of disturbance caused in an image isbecoming apparent.

For example, in a digital single lens reflex camera, an interchangeablelens includes a coil provided inside a motor circuit for driving thelens. A slight amount of leakage magnetic flex generated from such acoil may affect the image pickup element to thereby cause disturbance ofan image to be generated.

Conventionally, Japanese Patent Application Laid-open No. 2011-123432proposes that in order to shield a magnetic field from a magnetic fieldgeneration source located around an image pickup element, part of theimage pickup element is surrounded by a ferromagnetic substance havinghigh relative permeability such as permalloy.

A plate member of a ferromagnetic substance having high relativepermeability (such as permalloy, for example) exhibits a high magneticfield shielding effect if the surface area is large. However, it isexpensive compared with stainless or steel sheet generally used forcasings of electronic devices. As such, for inexpensive products, it isnot allowable to use an effective, large ferromagnetic substance havinghigh relative permeability. As such, it is desirable to have aconfiguration capable of effectively reducing the amount of a magneticfield reaching an image pickup element, even if the area of aferromagnetic material having high relative permeability is small.

In view of the above, an object of the present technology is to reducethe amount of a magnetic field reaching an image pickup element even ifthe area (cubic content) of a magnetic body, made of a ferromagneticmaterial having high relative permeability, is small.

SUMMARY OF THE INVENTION

An imaging device of the present technology includes an imaging opticalsystem; an image pickup element arranged opposite to the imaging opticalsystem, and configured to perform photoelectric conversion on an opticalimage formed by the imaging optical system; a magnetic field generationsource that generates a magnetic field when receiving an electriccurrent supplied; an annular first magnetic body; and a second magneticbody. The first magnetic body is arranged between the magnetic fieldgeneration source and the image pickup element, and has an openingthrough which light directed from the imaging optical system toward theimage pickup element passes. The second magnetic body is arranged at aposition which is on the side of the magnetic field generation sourcewith respect to the first magnetic body in an optical axis direction ofthe imaging optical system, and on the side of the magnetic fieldgeneration source with respect to the opening, while at least a portionthereof overlapping the first magnetic body when seen in the opticalaxis direction. The second magnetic body is made of a ferromagneticmaterial having higher relative permeability than that of the firstmagnetic body, and has a smaller area than that of the first magneticbody when seen in the optical axis direction.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a schematic configuration of an imagingdevice according to a first embodiment of the present technology.

FIGS. 2A and 2B are diagrams illustrating details of main part of theimaging device according to the first embodiment of the presenttechnology.

FIG. 3 is a diagram illustrating a measurement system for measuringrelative permeability.

FIG. 4 is a graph illustrating relative permeability with respect to thefrequency of SUS430.

FIG. 5 is a graph illustrating results of obtaining a magnetic fieldreaching an image pickup element through electromagnetic fieldsimulation.

FIG. 6 is a graph illustrating results of obtaining a magnetic fieldreaching an image pickup element through electromagnetic fieldsimulation.

FIG. 7 is a graph illustrating results of obtaining a magnetic fieldreaching an image pickup element through electromagnetic fieldsimulation.

FIGS. 8A and 8B are diagrams illustrating a schematic configuration ofan imaging device according to a second embodiment of the presenttechnology.

FIG. 9 is a diagram illustrating a schematic configuration of aninterchangeable lens according to a third embodiment of the presenttechnology.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

Hereinafter, an embodiment of the present technology will be describedin detail with reference to the drawings. FIG. 1 is a diagramillustrating a schematic configuration of a camera as an imaging deviceaccording to a first embodiment of the present technology. A digitalcamera (camera) 100 as an imaging device is a digital single lens reflexcamera, which includes a camera main body 200 that is a main body of theimaging device, and an interchangeable lens (lens barrel) 300 attachableto and detachable from the camera main body 200. In FIG. 1, theinterchangeable lens 300 is attached to the camera main body 200.Hereinafter, description will be given on the assumption that theinterchangeable lens 300 is attached to the camera main body 200.

The camera main body 200 includes a casing 201, and also includes amirror 222, a shutter 223, an imaging unit 202, and an image processingcircuit 224 which are disposed inside the casing 201. The camera mainbody 200 also includes a liquid crystal display 225 fixed to the casing201 so as to be exposed outside from the casing 201. The imaging unit202 includes an image pickup element 203 having a semiconductor unit(semiconductor chip) 231. The semiconductor unit 231 has a lightreceiving surface 231 a.

The interchangeable lens 300 includes a casing 301 that is aninterchangeable lens casing, and an imaging optical system 311 disposedinside the casing 301 and configured to form an optical image on thelight receiving surface 231 a of the image pickup element 203 when thecasing 301 (interchangeable lens 300) is attached to the casing 201. Theimaging optical system 311 is configured of a plurality of lenses.

The interchangeable lens 300 also includes an annular lens driving motor312 arranged around the imaging optical system 311, and a drive circuit313 for driving (operating) the lens driving motor 312. The drivecircuit 313 includes a printed wiring board formed in an annular shape,and a boosting coil 321 mounted on the printed wiring board.

The casing 301 has a lens-side mount 301 a having an opening formedtherein, and the casing 201 has a camera-side mount 201 a having anopening formed therein. By fitting the lens-side mount 301 a and thecamera-side mount 201 a, the interchangeable lens 300 (casing 301) isattached to the camera main body 200 (casing 201).

An arrow X direction illustrated in FIG. 1 is an optical axis directionof the imaging optical system 311, which is vertical to the lightreceiving surface 231 a of the image pickup element 203.

Light traveling in the arrow X direction from the imaging optical system311 is guided into the casing 201 through an opening in the lens drivingmotor 312, an opening in the drive circuit 313, the opening in thelens-side mount 301 a of the casing 301, and the opening in thecamera-side mount 201 a of the casing 201.

Inside the casing 201, the mirror 222, the shutter 223, and the like areprovided along the arrow X direction in front side in the arrow Xdirection (the light receiving surface 231 a side) of the imaging unit202.

The image pickup element 203 is an image sensor (solid-state imagesensor) such as a CMOS image sensor or a CCD image sensor which performsphotoelectric conversion on an optical image formed by the imagingoptical system 311. The image pickup element 203 is formed to have aquadrangle outer shape in a front view (seen from the arrow X directionvertical to the light receiving surface 231 a of the image pickupelement 203).

The image pickup element 203 is arranged inside the casing 201 such thatwhen the interchangeable lens 300 is attached to the casing 201, thelight receiving surface 231 a faces the imaging optical system 311 viathe mirror 222, the shutter 223, and the like.

The image pickup element 203 performs photoelectric conversion on anoptical image formed on the light receiving surface 231 a by the imagingoptical system 311 when the interchangeable lens 300 is attached to thecasing 201, and outputs an image signal to the image processing circuit224. The image processing circuit 224 performs image processing on theobtained image data, and outputs it to the liquid crystal display 225, amemory (not illustrated), and the like.

The coil 321 is a magnetic field generation source which generates amagnetic field when an electric current is supplied, and is a source ofmagnetic field noise with respect to the image pickup element 203.

FIGS. 2A and 2B are diagrams illustrating the coil 321 and the imagingunit 202 which are main part of the camera 100. FIG. 2A is a front viewof the coil 321 and the imaging unit 202 seen in the arrow X direction.FIG. 2B is a side view of the coil 321 and the imaging unit 202 seen ina direction orthogonal to the arrow X direction. The image pickupelement 203 includes the semiconductor unit 231 and a package substrate232 on which the semiconductor unit 231 is mounted, in which a pluralityof terminals 233 is fixed on the package substrate 232 and are mountedon (joined by soldering to) the printed wiring board 204. The packagesubstrate 232 is formed of a ceramic substrate, a resin substrate, aprinted wiring board, or the like.

The imaging unit 202 includes a frame-like (annular) magnetic member 210having an opening H disposed between the coil 321 that is a magneticfield generation source, and the image pickup element 203. The magneticmember 210 is arranged adjacent to the image pickup element 203.Specifically, as illustrated in FIG. 2B, a first magnetic body 211 isarranged adjacent to the image pickup element 203 on the side where thecoil 321 is arranged with respect to the image pickup element 203, inthe arrow X direction.

The magnetic member 210 includes the first magnetic body 211, and asecond magnetic body 212 made of a ferromagnetic material of higherrelative permeability than that of the first magnetic body 211 andhaving a smaller area than that of the first magnetic body 211 when seenin the optical axis direction of the imaging optical system. Further, aregion where the second magnetic body is arranged includes a regionnearest to the coil 321 that is a magnetic field generation source ofthe annular magnetic member 210.

The opening H is formed to have a size in which light travelling fromthe imaging optical system 311 to the light receiving surface 231 a ofthe image pickup element 203 passes through. Specifically, the opening His formed to have a larger area than that of the light receiving surface231 a when seen in the arrow X direction. Further, when seen in thearrow X direction, the opening H is formed to have a smaller area thanthat of the outer shape of the image pickup element 203 (the surface ofthe package substrate 232 on which the semiconductor unit 231 ismounted). The light receiving surface 231 a is formed to be in aquadrangle shape when seen in the arrow X direction, and the opening His also formed to be in a quadrangle shape when seen in the arrow Xdirection.

Further, the imaging unit 202 includes the second magnetic body 212arranged at a position of the coil 321 side in the arrow X directionwith respect to the first magnetic body 211. The first magnetic body 211has a surface 211 a of the side where the coil 321 is arranged in thearrow X direction, and the second magnetic body 212 is arranged adjacentto the surface 211 a. In that case, it is preferable that the secondmagnetic body 212 is arranged with a slight gap with respect to thefirst magnetic body 211, or arranged to be in contact with the firstmagnetic body 211. While it is only necessary that the gap between thefirst magnetic body 211 and the second magnetic body 212 has magneticcoupling, it is preferable to bring the first magnetic body 211 and thesecond magnetic body 212 into contact with each other because themagnetic resistance is reduced.

Further, the first magnetic body 211 may be annular or have a structurein which a portion of the annular shape is cut off. In the case of astructure in which a portion of the annular shape is cut off, it ispreferable that the first magnetic body 211 and the second magnetic body212 are integrated, and that the shape of the integrated first magneticbody 211 and second magnetic body 212 is annular. Further, “annular” inthis context may be toric, quadrangle annular, or other annular shapes.

As illustrated in FIG. 2A, the second magnetic body 212 is arranged at aposition of the coil 321 side with respect to the opening H when seen inthe arrow X direction, while at least a portion thereof (the whole inthe present embodiment) overlapping the first magnetic body 211.Specifically, the second magnetic body 212 is arranged adjacent to oneside, nearest to the coil 321, of the four sides of the opening H. Thismeans that the second magnetic body 212 is arranged on the frame portionof an opening side nearest to the coil 321, on the surface 211 a of thecoil side of the first magnetic body 211.

The first magnetic body 211 and the second magnetic body 212 are made ofa ferromagnetic material and formed in a plate shape or a film shape.The second magnetic body 212 is made of a ferromagnetic material havinghigher relative permeability than that of the first magnetic body 211.The second magnetic body 212 is formed to have a smaller area than thatof the first magnetic body 211 when seen in the arrow X direction.Further, the second magnetic body 212 is formed to be thinner in thearrow X direction than the first magnetic body 211.

It is preferable that the first magnetic body 211 is formed of stainlessSUS430 which is made of a material having lower relative permeability.As the first magnetic body 211 is not an expensive material having highrelative permeability such as permalloy which is typically used as amagnetic body, it is possible to suppress an increase in the cost evenif the first magnetic body 211 is used in a large area.

It should be noted that besides SUS430, as the first magnetic body 211,it is also possible to use SUS630, SPCC steel (cold rolled steel), orsome galvanized steel such as Silver Top (registered trademark), whichis a magnetic body having low relative permeability. Here, a magneticbody having low relative permeability means one having relativepermeability of not less than 50 but not more than 1000, specifically.This can be preferably used as a material of the first magnetic body211. This means that the first magnetic body 211 may be formed includingat least one of SUS430, SUS630, SPCC steel, and some galvanized steel.In other words, the first magnetic body 211 may be configured of any oneof SUS430, SUS630, SPCC steel, and some galvanized steel, or acombination of two or more of them. For example, the first magnetic body211 may be configured of a combination of SUS430 and SUS630. However, asthe first magnetic body 211, one having relative permeability of almost1 which is not a so-called magnetic body, such as aluminum, copper,SUS304, or conductive plastic, is unable to be used.

On the other hand, the second magnetic body 212 is formed of ananocrystal soft magnetic material such as Finemet (registeredtrademark) which is a ferromagnetic material having higher relativepermeability than that of the first magnetic body 211. Besides, as thesecond magnetic body 212, it is also possible to use permalloy havinghigh permeability, amorphous magnetic material, ferrite, electromagneticsteel, a noise suppression sheet having high permeability such asBusteraid (registered trademark)(containing magnetic powder, magneticfiller, or magnetic film), and the like. This means that it is onlynecessary that the second magnetic body 212 is formed by containing atleast one of nanocrystal soft magnetic material, permalloy, amorphousmagnetic material, ferrite, electromagnetic steel, and a noisesuppression sheet having high permeability (containing magnetic powder,magnetic filler, or magnetic film). In other words, the second magneticbody 212 may be any one of nanocrystal soft magnetic material,permalloy, amorphous magnetic material, ferrite, electromagnetic steel,and a noise suppression sheet having high permeability, or a combinationof two or more of them. The noise suppression sheet is one containingmagnetic powder, magnetic filler, or magnetic film.

As the area of the second magnetic body 212, seen in the arrow Xdirection, is significantly smaller than that of the first magnetic body211, it is possible to suppress an increase in the cost as a component.

Here, description will be added regarding relative permeability ofSUS430 in a plate shape which constitutes the first magnetic body 211.The relative permeability of SUS430 was measured under a condition thatinitial permeability was calculated by applying a magnetic flux densityof not more than 1 μT specified by JIS 2561C. However, JIS 2561Cspecifies to perform measurement using a ring-shaped measurement sample.As such, permeability of a plate-like magnetic body to be actually usedis unable to be calculated accurately with such a measurement method.Accordingly, it is necessary to use a tool capable of measuring aplate-like sample.

FIG. 3 is a diagram illustrating a measurement system for measuringrelative permeability. A double yoke frame 41 (yokes 412 and a coil 411surrounded by the yokes 412) illustrated in FIG. 3 is one used in“electromagnetic steel plate veneer magnetism testing method” of JISC2556, and a measurement sample 413 formed in a plate shape is insertedin the frame. To the coil 411 of the double yoke frame 41, an LCR meter42 (impedance analyzer is also acceptable) is connected to therebyobtain an inductance value. With reference to the inductance value of astate where the sample is not inserted, the real part p′ of permeabilitywas calculated from the inductance value and the resistance value whenthe measurement sample 413 was inserted, using the following Expression(1).

Expression  1                                      $\begin{matrix}{\mu^{\prime} = {\frac{L\left( {L_{eff} - L_{w}} \right)}{\mu_{0}N^{2}A}.}} & {{Expression}\mspace{14mu}(1)}\end{matrix}$

Here, N=the number of windings of the coil, vacuum permeabilityμ₀=4π×10⁷ (H/m), A=sectional area of measurement sample, L=length ofmeasurement sample, L_(eff)=inductance measurement value obtained by LCRmeter, and L_(w)=inductance measurement value when sample is notinserted.

FIG. 4 illustrates relative permeability of stainless SUS430 obtained bythis method. FIG. 4 is a graph illustrating the relative permeabilitywith respect to the frequency of SUS430. The horizontal axis shows thefrequency and the vertical axis shows the relative permeability. In thecase of low frequencies, relative permeability is almost 150 (no unit).In the case of high frequencies, as a magnetic field is less likely toenter due to an effect of an eddy current, it is found that effectiverelative permeability drops.

It is found that as the thickness is increased to 0.3 mm, 0.5 mm, and0.9 mm, the relative permeability begins to drop in lower frequencies.Accordingly, a smaller thickness is advantageous for obtaining higherrelative permeability in higher frequencies.

Accordingly, in the present embodiment, if the thickness of the firstmagnetic body 211 is 0.9 mm and the current flowing in the coil 321 isabout 30 kHz, the relative permeability of the first magnetic body 211is about 50 (no unit), according to FIG. 4. By performing relativepermeability measurement depending on this thickness, it is possible toselect a magnetic material of a plate member corresponding to thethickness to be used actually, as the first magnetic body 211 of lowpermeability.

Further, the relative permeability at 30 kHz of a nanocrystal softmagnetic material, which is the second magnetic body 212, is about 20000(no unit). Other materials such as permalloy, electromagnetic steel,ferrite, and pure iron, having high relative permeability, generallytake values shown in Table 1, although depending on the frequency.

TABLE 1 Relative permeability Nanocrystal soft magnetic 20000-200000material Permalloy 2500-70000 Electromagnetic steel 400-3200 Ferrite400-3000 Pure iron 300-1000 Magnetic stainless, Steel sheet 150-500 

Among these materials, ferromagnetic materials having higher relativepermeability than that of the first magnetic body 211 can be used as thesecond magnetic body 212. Especially, one having relative permeabilitynot less than 1000 (no unit) but less than 200000 which is the limit ofindustrial production can be preferably used as a material of the secondmagnetic body 212.

According to the present embodiment, the following action is made. Thatis, in order to rotate the lens driving motor 312, when an AC current ofa driving frequency 30 kHz flows in the boosting coil 321, for example,a slight leakage magnetic field is generated in the space around thecoil 321. The generated leakage magnetic field propagates the spacewhile being attenuated.

As the magnetic field reaching near the image pickup element 203 is analternate current, the direction is switched as constant vibration whilebeing switched by the time period. From the viewpoint of a magneticcircuit, in FIGS. 2A and 2B, the magnetic field reaching near the imagepickup element 203 is shunted to two types of paths, namely, a magnetictransmission path R1 reaching the image pickup element 203 shown bydotted-line arrows, and a magnetic transmission path R2 passing throughthe magnetic bodies 211 and 212 shown by solid-line arrows.

As a shunt ratio of the magnetic field varies according to the magneticresistance of each of the paths R1 and R2, it is important to make themagnetic resistance of the magnetic transmission path R2, passingthrough the magnetic bodies 211 and 212, lower than the magneticresistance of the magnetic transmission path R1 reaching the imagepickup element 203. In the magnetic resistance of the entire magnetictransmission path R2 passing through the magnetic bodies 211 and 212,magnetic resistance of a region where the second magnetic body 212 isprovided, in which the magnetic field should be transmitted by beingbent in a horizontal direction, is dominant. By reducing the magneticresistance of such a region by providing the second magnetic body 212having high relative permeability in a long length in a horizontaldirection, it is possible to reduce the magnetic resistance of theentire path R2 passing through the magnetic bodies 211 and 212.

In other words, even if magnetic resistance of another portion (forexample, the frame portions on both right and left sides of the firstmagnetic body 211, the lower-side frame portion, or the inner peripheralsurface on the image pickup element side of the upper-side frameportion) is reduced, while the magnetic resistance of the entiremagnetic bodies 211 and 212 can be reduced a little, it cannot bereduced effectively.

In the present embodiment, by combining the first magnetic body 211 andthe second magnetic body 212, it is possible to reduce the magneticresistance of the entire path R2 passing through the magnetic bodies 211and 212. Accordingly, the magnetic field shunted to the magnetictransmission path R2 is increased, whereby it is possible to reduce themagnetic field shunted to the magnetic transmission path R1 reaching theimage pickup element 203. Consequently, it is possible to reduce theamount of a leakage magnetic field, generated from the boosting coil321, reaching the image pickup element 203. As such, even if thesemiconductor unit 231 of the image pickup element 203 performsoperation to read an image signal, the influence by the magnetic fieldis less, image disturbance is less likely to be caused, and an originalimage signal is read.

The effect of suppressing image disturbance was tested in the digitalsingle lens reflex camera 100 by capturing a dark image in a state offeeding an AC current to the coil 321 with no incident light. In thecase of a dark image, as the entire image must show a certain level ofluminance, deviation from the luminance value (deviation amount) is usedhere as an image disturbance amount. Assuming that an image disturbanceamount without the first magnetic body 211 and the second magnetic body212 is 100%, in the camera 100 of the present embodiment having thefirst magnetic body 211 and the second magnetic body 212, the imagedisturbance amount was reduced to about 72%.

Next, effects provided by the shape of the second magnetic body 212 willbe described in detail based on examples.

Example 1

In FIG. 2A illustrating a front view of the image pickup element 203,the image pickup element 203 having the semiconductor unit 231 of 25 mmlaterally wide and 18 mm vertically wide was used. Around the imagepickup element 203, the first magnetic body 211 (conductivity σ=1.0×10⁷(S/m), relative permeability 50 (no unit)) was provided. The firstmagnetic body 211 had an opening H of 36 mm laterally wide and 25 mmvertically wide, and the frame shape thereof was 7 mm laterally wide and0.9 mm thick. Away from the first magnetic body 211 by 0.1 mm, thesecond magnetic body 212 (conductivity o=1.0×10⁷ (S/m), relativepermeability 10000 (no unit)) in a rectangle shape of 20 mm laterallywide, 7 mm vertically wide, and 18 μm thick was provided. The coil 321generating a magnetic field was arranged from a position of 19.5 mmvertically upward of the center of the image pickup element 203 and 10mm right horizontally, to a position of 50 mm in a front directionorthogonal to the sheet, such that the coil winding axis matched adirection orthogonal to the sheet.

It should be noted that at a position of 1.7 mm behind the image pickupelement 203, a conductor, which was not a magnetic body, of 42 mmlaterally wide, 38 mm vertically wide, and 0.07 mm thick was provided asa ground pattern in the printed wiring board 204. This conductor hadconductivity σ=5.7×10⁷ (S/m), and relative permeability 1.0 (no unit).

Example 2

The second magnetic body 212 of 30 mm laterally wide, longer than thehorizontal width 25 mm of the semiconductor unit 231 of the image pickupelement 203, was provided. As the other aspects were the same as thoseof Example 1, the description is omitted.

Example 3

The second magnetic body 212 of 50 mm laterally wide, longer than thehorizontal width 36 mm of the opening H of the magnetic member 210, wasprovided. As such, the second magnetic body 212 was disposed along oneside of the opening H of the magnetic member 210, and the length in adirection along one side was set to be longer than one side of theopening H. As the other aspects were the same as those of Example 1, thedescription is omitted.

Example 4

The second magnetic body 212 of 1 mm vertically wide and 50 mm laterallywide was provided. As the other aspects were the same as those ofExample 1, the description is omitted.

Example 5

The second magnetic body 212 of 2 mm vertically wide and 50 mm laterallywide was provided. As the other aspects were the same as those ofExample 1, the description is omitted.

Example 6

The second magnetic body 212 of 3 mm vertically wide and 50 mm laterallywide was provided. As the other aspects were the same as those ofExample 1, the description is omitted.

Comparative Example 1

Only the first magnetic body 211 was provided, without the secondmagnetic body 212. As the other aspects were the same as those ofExample 1, the description is omitted.

Regarding respective Examples 1 to 6 and Comparative Example 1, amagnetic field reaching the semiconductor unit 231 of the image pickupelement 203 was obtained using commercial electromagnetic fieldsimulation (ANSYS “Maxwell 3D”). The current applied to the coil 321 wasa sine wave having a frequency of 30 kHz.

FIG. 5 is a graph illustrating the results obtained from theelectromagnetic field simulation of the magnetic field that reached thesemiconductor unit 231 of the image pickup element 203 in Examples 1 to3 and Comparative Example 1. As illustrated in FIG. 5, in Examples 1 to3, the magnetic field reaching the semiconductor unit 231 of the imagepickup element 203 was reduced, compared with Comparative Example 1.Especially, it was reduced largely in Example 3. This means that byproviding the second magnetic body 212 of high relative permeabilityhaving a horizontal width longer than the length of the opening H of themagnetic member 210, the magnetic resistance in transmitting themagnetic field in a lateral width direction of the entire magneticbodies 211 and 212 was reduced.

FIG. 6 is a graph illustrating the results obtained from theelectromagnetic field simulation of the reached magnetic field inExamples 3 to 6 and Comparative Example 1. As illustrated in FIG. 6, inExamples 3 to 6, the magnetic field that reached the semiconductor unit231 of the image pickup element 203 was reduced, compared with thereached magnetic field of Comparative Example 1.

Especially, in Example 4, the reached magnetic field was reducedalthough the vertical width of the second magnetic body 212 having highrelative permeability was 1 mm and the area was only 50 mm², comparedwith Example 1 having the area of 140 mm².

This means that by providing the second magnetic body 212 of highrelative permeability having a lateral width longer than the length ofthe opening H of the magnetic member 210 even though the vertical widthis narrow, the magnetic resistance in transmitting the magnetic field ina lateral width direction is effectively reduced. As such, in the caseof further reducing the area of the second magnetic body 212 of highrelative permeability, it is important to have a lateral width longerthan the side length of the opening H of the magnetic member 210, eventhough the vertical width is narrow.

Further, while it is desirable that a separated distance between thefirst magnetic body 211 and the second magnetic body 212 is short, theresults show that the magnetic field amount reaching the image pickupelement 203 is almost the same if the distance is within a range from0.1 mm to 3 mm.

Next, influence of the relative permeability of the first magnetic body211 will be described. FIG. 7 is a graph illustrating the resultobtained by the electromagnetic field simulation of the magnetic fieldthat reached the image pickup element 203, while changing the relativepermeability of the first magnetic body from 50 in Example 3. The secondmagnetic body 212 and the other conditions were the same as those ofExample 3. However, only magnetic field in a vertical directionhorizontal to a notably large sensor surface (light receiving surface231 a), in the magnetic field of the magnetic transmission path R1, wasextracted. It should be noted that the relative permeability of thesecond magnetic body 212 was assumed to be 40000.

When the relative permeability of the first magnetic body 211 was 1 (thecase of so-called non-magnetic body) and there was no second magneticbody, the reached magnetic field was 0.138 μT. Meanwhile, when therelative permeability of the first magnetic body 211 was 1 and there wasthe second magnetic body 212, the reached magnetic field was 0.135 μT,as illustrated in FIG. 7. As such, even with the second magnetic body212, magnetic field bypassing effect was hardly obtained.

In the case were the relative permeability of the first magnetic body211 became 50, magnetic field bypassing effect began to appear rapidly.With the relative permeability higher than that, the magnetic field thatreached the image pickup element 203 was reduced as the relativepermeability was increased.

Accordingly, as the first magnetic body 211, higher relativepermeability is better. It is preferable that the relative permeabilityis 50 or higher. However, if the relative permeability is higher than1000, a magnetic material is expensive. As such, it is preferable to usea material having relative permeability of lower than 1000 in practice.

Accordingly, the relative permeability of the first magnetic body 211 ispreferably not less than 50 but less than 1000 in the driving frequencyof the coil 321. Further, as described above, the relative permeabilityof the second magnetic body 212 is preferably not less than 1000 butless than 200000 in the driving frequency of the coil 321.

As described above, by using the first magnetic body 211 and the secondmagnetic body 212 having a smaller area and higher relative permeabilitythan those of the first magnetic body 211, it is possible to reduce themagnetic field that reaches the image pickup element 203. As such, imagedisturbance caused by the image pickup element 203 can be suppressed.Further, as the area of the second magnetic body 212 having highrelative permeability, which is expensive, can be reduced, it ispossible to suppress image disturbance with an inexpensiveconfiguration.

It should be noted that the present technology is not limited to theembodiment described above, and various changes can be made within thetechnical concept of the present technology. For example, even if thedriving frequency of an electric current flowing in the coil, thearrangement, and the number are different, the present technology can becarried out by arranging the magnetic bodies corresponding to the case.Further, as for the first and second magnetic bodies, it is alsopossible to use materials other than those described in the embodimentby performing permeability measurement described herein.

Further, in the embodiment described above, description has been givenon the case where the interchangeable lens 300 is configured to bedetachable from the camera main body 200, the coil 321 is provided tothe casing 301 of the interchangeable lens 300, and the first and secondmagnetic bodies 211 and 212 are provided to the casing 201 of the cameramain body 200. However, the present technology is not limited to thisconfiguration. The present technology is also applicable to an imagingdevice in which a lens is integrally installed in the imaging devicemain body. For example, the present technology is applicable not only toa digital single lens reflex camera but also a compact digital camera.In that case, a coil and first and second magnetic bodies are providedto the casing of the camera.

As such, according to the present embodiment, by using a first magneticbody and a second magnetic body having a smaller area and higherrelative permeability than those of the first magnetic body, it ispossible to reduce the magnetic field that reaches the image pickupelement.

Second Embodiment

Next, a second embodiment of the present technology will be describedwith reference to FIGS. 8A and 8B. FIGS. 8A and 8B are diagramsillustrating a schematic configuration of a camera as an imaging deviceaccording to the second embodiment of the present technology. A coil502, which is a magnetic field generation source of a power sourceconversion circuit 501 serving as a power source circuit, is disposedinside the casing 201 of the camera main body 200.

The imaging unit 202 includes a frame-like (annular) first magnetic body505 having an opening H arranged between the coil 502 that is a magneticfield generation source and the image pickup element 203. The firstmagnetic body 505 is arranged adjacent to the image pickup element 203.More specifically, the first magnetic body 505 is arranged adjacent tothe image pickup element 203 on the side where the coil 502 is disposedwith respect to the image pickup element 203 in the arrow X direction,as illustrated in FIG. 8B.

The imaging unit 202 also includes a second magnetic body 504 arrangedat a position of the coil 502 side with respect to the first magneticbody 505. The first magnetic body 505 has a surface on the side wherethe coil 502 is arranged in the arrow X direction, and the secondmagnetic body 504 is arranged adjacent to the surface. In that case, itis preferable that the second magnetic body 504 is arranged to have aslight gap with the first magnetic body 505 or is brought into contactwith the first magnetic body 505. It is more preferable to bring thefirst magnetic body 505 and the second magnetic body 504 into contactwith each other, because the magnetic resistance is reduced.

As illustrated in FIG. 8A, the second magnetic body 504 is arranged at aposition of the coil 502 side with respect to the opening H when seen inthe arrow X direction, while at least a portion thereof (the whole inthe present embodiment) overlapping the first magnetic body 505.Specifically, the second magnetic body 504 is arranged adjacent to oneside, nearest to the coil 502, of the four sides of the opening H. Thismeans that the second magnetic body 504 is arranged on the frame portionof an opening side nearest to the coil 502, on the surface of the coilside of the first magnetic body 505.

The first magnetic body 505 and the second magnetic body 504 are made ofa ferromagnetic material and formed in a plate shape or a film shape.The second magnetic body 504 is made of a ferromagnetic material havinghigher relative permeability than that of the first magnetic body 505.The second magnetic body 504 is formed to have a smaller area than thatof the first magnetic body 505 when seen in the arrow X direction.Further, the second magnetic body 504 is formed to be thinner in thearrow X direction than the first magnetic body 505.

According to this configuration, most of the magnetic field 503,generated from the coil 502 that is a magnetic field generation source,passes through the second magnetic body 504 having low magneticresistance, and subsequently passes through the first magnetic body 505.As such, the magnetic field reaching the image pickup element 203 can bereduced. The materials of the first magnetic body and the secondmagnetic body are selectable, which is the same as the case of the firstembodiment.

In this way, by using the first magnetic body 505 and the secondmagnetic body 504 having a smaller area and higher relative permeabilitythan those of the first magnetic body 505, it is possible to reduce themagnetic field reaching the image pickup element 203. As such, imagedisturbance caused by the image pickup element 203 can be suppressed.Further, as the area of the second magnetic body 504 having highrelative permeability, which is expensive, can be reduced, it ispossible to suppress image disturbance with an inexpensiveconfiguration.

As in the present embodiment, the present technology is applicable evenin the case where a magnetic field generation source is provided to thecasing of the camera main body, and the camera main body corresponds tothe imaging device.

Third Embodiment

Next, a third embodiment of the present technology will be describedwith reference to FIG. 9. FIG. 9 is a diagram illustrating a schematicconfiguration of an interchangeable lens according to the thirdembodiment of the present technology. In the third embodiment, the coil321 that is a magnetic field generation source of the drive circuit 313is disposed inside the casing 301 of the interchangeable lens 300. Theinterchangeable lens 300 (casing 301) is configured to be detachablefrom the imaging device main body (camera main body).

In FIG. 9, an annular first magnetic body 602 having an opening isarranged between the coil 321 that is a magnetic field generationsource, and an image pickup element (not illustrated). Further, a secondmagnetic body 601 is arranged at a position on the coil 321 side withrespect to the first magnetic body 602. The first magnetic body 602 hasa surface on the side where the coil 321 is arranged in the arrow Xdirection, and the second magnetic body 601 is disposed adjacent to thesurface. In that case, it is preferable that the second magnetic body601 is arranged to have a slight gap with the first magnetic body 602 oris brought into contact with the first magnetic body 602. It is morepreferable to bring the first magnetic body 602 and the second magneticbody 601 into contact with each other, because the magnetic resistanceis reduced.

As illustrated in FIG. 9, the second magnetic body 601 is arranged at aposition of the coil 321 side with respect to the opening when seen inthe arrow X direction, while at least a portion thereof (the whole inthe present embodiment) overlapping the first magnetic body 602.Specifically, the second magnetic body 601 is arranged on a frameportion adjacent nearest to the coil 321, of the sides of the opening.

The first magnetic body 602 and the second magnetic body 601 are made ofa ferromagnetic material and formed in a plate shape or a film shape.The second magnetic body 601 is made of a ferromagnetic material havinghigher relative permeability than that of the first magnetic body 602.The second magnetic body 601 is formed to have a smaller area than thatof the first magnetic body 602 when seen in the arrow X direction.Further, the second magnetic body 601 is formed to be thinner in thearrow X direction than the first magnetic body 602.

According to this configuration, most of the magnetic field 600,generated from the coil 321 that is the magnetic field generationsource, passes through the second magnetic body 601 having low magneticresistance, and subsequently passes through the first magnetic body 602.As such, the magnetic field reaching the image pickup element (notillustrated) can be reduced. The materials of the first magnetic body602 and the second magnetic body 601 are selectable, which is the sameas the case of the first embodiment.

In this way, by using the first magnetic body 602 and the secondmagnetic body 601 having a smaller area and higher relative permeabilitythan those of the first magnetic body 602, it is possible to reduce themagnetic field reaching the image pickup element. As such, imagedisturbance caused by the image pickup element can be suppressed.Further, as the area of the second magnetic body 601 having highrelative permeability, which is expensive, can be reduced, it ispossible to suppress image disturbance with an inexpensiveconfiguration.

As in the present embodiment, present technology is applicable even inthe case where an interchangeable lens has first and second magneticbodies.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

What is claimed is:
 1. An imaging device comprising: a magnetic fieldgeneration source that generates a magnetic field when receiving anelectric current supplied; and an image pickup element including alight-receiving unit configured to perform photoelectric conversion onincident light; and, a magnetic member arranged between magnetic fieldgeneration source and the image pickup element, wherein the magneticmember includes a first magnetic body and a second magnetic body, thesecond magnetic body being made of a ferromagnetic material havinghigher relative permeability than relative permeability of the firstmagnetic body, and the second magnetic body is arranged nearer than thefirst magnetic body to the magnetic field generation source.
 2. Theimaging device according to claim 1, wherein the second magnetic body isarranged in contact with a surface of a side opposite to the magneticfield generation source of the first magnetic body and the secondmagnetic body having a smaller area than an area of the first magneticbody.
 3. The imaging device according to claim 1, wherein the magneticmember is arranged around the light-receiving unit, and the secondmagnetic body is arranged along a side of the image pickup element nearthe magnetic field generation source.
 4. The imaging device according toclaim 1, wherein the relative permeability of the first magnetic body isnot less than 50 but less than 1000 in a driving frequency of themagnetic field generation source, and the relative permeability of thesecond magnetic body is not less than 1000 but less than 200000 in thedriving frequency of the magnetic field generation source.
 5. Theimaging device according to claim 1, wherein the first magnetic bodyincludes at least one of SUS430 steel, SUS630 steel, and cold rolledSteel (SPCC steel), and the second magnetic body includes at least oneof nanocrystal soft magnetic material, permalloy, amorphous magneticmaterial, ferrite, and electromagnetic steel.
 6. The imaging deviceaccording to claim 1, wherein the imaging device is a camera.
 7. Animaging device comprising: a casing to and from which an interchangeablelens is attachable and detachable, the interchangeable lens includingmagnetic field generation source that generates a magnetic field whenreceiving an electric current supplied; an image pickup element to bearranged inside the casing, and including a light-receiving unitconfigured to perform photoelectric conversion on incident light; and amagnetic member to be arranged inside the casing at a position on themagnetic field generation source toward the image pickup element whenthe interchangeable lens is attached to the casing, wherein the magneticmember includes a first magnetic body and a second magnetic body, thesecond magnetic body being made of a ferromagnetic material havinghigher relative permeability than relative permeability of the firstmagnetic body, and the second magnetic body is arranged nearer than thefirst magnetic body to the magnetic field generation source.
 8. Theimaging device according to claim 7, wherein the second magnetic bodyhas a smaller area than an area of the first magnetic body.
 9. Theimaging device according to claim 7, wherein the magnetic member isarranged around the light-receiving unit, and the second magnetic bodyis arranged along a side of the image pickup element near the magneticfield generation source.
 10. An imaging device comprising: a casing toand from which an interchangeable lens is attachable and detachable; animage pickup element to be arranged inside the casing, and including alight-receiving unit configured to perform photoelectric conversion onincident light; a magnetic field generation source provided to thecasing, the magnetic field generation source generating a magnetic fieldwhen receiving an electric current supplied; and a magnetic memberarranged on the magnetic field generation source toward the image pickupelement, wherein the magnetic member includes a first magnetic body anda second magnetic body, the second magnetic body being made of aferromagnetic material having higher relative permeability than relativepermeability of the first magnetic body, and the second magnetic body isarranged nearer than the first magnetic body to the magnetic fieldgeneration source.
 11. The imaging device according to claim 10, whereinthe second magnetic body is arranged in contact with a surface of a sideopposite to the magnetic field generation source of the first magneticbody and the second magnetic body having a smaller area than an area ofthe first magnetic body.
 12. The imaging device according to claim 10,wherein the magnetic member is arranged around the light-receiving unit,and the second magnetic body is arranged along a side of the imagepickup element near the magnetic field generation source.
 13. Aninterchangeable lens comprising: an interchangeable lens casingincluding a mount attachable to and detachable from an imaging devicemain body including an image pickup element; a magnetic field generationsource arranged inside the interchangeable lens casing, the magneticfield generation source generating a magnetic field when receiving anelectric current supplied; and a magnetic member arranged between themagnetic field generation source and the mount, wherein the magneticmember includes a first magnetic body and a second magnetic body, thesecond magnetic body being made of a ferromagnetic material havinghigher relative permeability than relative permeability of the firstmagnetic body, and the second magnetic body is arranged nearer than thefirst magnetic body to the magnetic field generation source.
 14. Theimaging device according to claim 13, wherein the second magnetic bodyis arranged in contact with a surface of a side opposite to the magneticfield generation source of the first magnetic body and the secondmagnetic body having a smaller area than an area of the first magneticbody.
 15. The imaging device according to claim 13, wherein the magneticmember is annularly arranged.
 16. The imaging device according to claim1, wherein a region in which the second magnetic body is arrangedincludes a region nearest to the magnetic field generation source of themagnetic member.
 17. The imaging device according to claim 1, whereinthe imaging device includes a lens barrel including an imaging opticalsystem and the magnetic field generation source, and the magnetic memberis arranged between the image pickup element and the imaging opticalsystem.
 18. An imaging device comprising: a lens barrel comprised of animaging optical system and a magnetic field generation source thatgenerates a magnetic field when receiving an electric current supplied;an image pickup element including a light-receiving unit configured toperform photoelectric conversion on incident light; and a magneticmember arranged between the imaging optical system and the image pickupelement, wherein the magnetic member includes a first magnetic body anda second magnetic body, the second magnetic body being made of aferromagnetic material having higher relative permeability than relativepermeability of the first magnetic body, and the second magnetic body isarranged nearer than the first magnetic body to the magnetic fieldgeneration source.
 19. The imaging device according to claim 18, whereinthe magnetic field generation source is a drive circuit that drives theimaging optical system or a coil included in a motor.
 20. The imagingdevice according to claim 18, wherein the imaging device is a camera.